In present-day semiconductor devices, various active attempts, such as fine patterning and the use of novel materials, are being made to increase speed and reduce power consumption. Fine patterning of semiconductor devices involves dry etching using fluorocarbon (referred to hereinafter also as “FC”) gas or hydrofluorocarbon (referred to hereinafter also as “HFC”) gas plasmas.
It is commonly known that, with FC gas plasmas having an unsaturated bond or a cyclic structure including two or more carbon atoms, such as C4F8, C4F6, and C5F8, CFx radicals are deposited as a fluorocarbon polymer on, for example, a silicon nitride film (referred to hereinafter also as “SiN”), a polycrystalline silicon film (referred to hereinafter also as “polysilicon” or “Poly-Si”), or a resist, and the deposit serves as a protection film, thus allowing a silicon oxide film (referred to hereinafter also as “SiOm” (wherein m represents a natural number)) to be selectively etched relative to the aforementioned films.
It is also known that a silicon nitride film can be selectively etched relative to, for example, a silicon oxide film or a polysilicon film by using a HFC gas including one carbon atom, such as CHF3, CH2F2, and CH3F.
Patent Literature 1 discloses a technique for etching, with high selectivity, a silicon nitride film relative to a silicon oxide film and a silicon film by using an unsaturated fluorohydrocarbon compound represented by CxHyFz (wherein x=3, 4, or 5, y+z≤2x, and y>z) as the etching gas.
Patent Literature 2 discloses a technique for selectively etching a silicon-based material, such as a silicon oxide film or a silicon-containing low dielectric constant film (referred to hereinafter also as “low-k film”), relative to a mask, such as silicon or a resist, with a C4F6 or C5F8 gas plasma. In the technique disclosed in this Patent Literature, the C4F6 or C5F8 gas plasma produces a large amount of CF+ and radicals including three or more carbon atoms in the skeleton thereof (polymer radicals produced from CF3CF═CFCF and CFCF═CF2 fragments). The technique disclosed in this Patent Literature is also characteristic in that, although CF+ has a low etching efficiency, damage to the resist and silicon is minimal, and that the radicals including three or more carbon atoms in the skeleton thereof form a fluorocarbon polymer film having low density. The technique disclosed in this Patent Literature is characteristic in that, by employing the aforementioned ions and radicals in a balanced manner, a silicon oxide film or a silicon-containing low dielectric constant film can be selectively etched without damaging the mask, such as the resist or silicon. The Patent Literature also describes that it is also possible to additionally achieve such effects as improved selectivity and low boiling point by replacing, with hydrogen, a portion of the fluorine atoms in the fluorocarbon gas having two double bonds, such as C4F6 or C5F8.
Patent Literature 3 discloses, in relation to the etching of hole structures patterned by a resist in a multilayer structure including a silicon oxide film and a silicon nitride film, a technique that allows selective etching of a silicon oxide film and a silicon nitride film relative to a resist by using a HFC-based gas plasma represented by CaHbFc (wherein a is from 3 to 5, b is from 1 to 2, and c is from 3 to 10). The decomposition of CaHbFc (wherein a is from 3 to 5, b is from 1 to 2, and c is from 3 to 10) in a plasma produces CF radicals originating from fluorocarbons and CH radicals originating from hydrocarbons. The CF radicals etch the silicon oxide film without reacting with the silicon nitride film. The CH radicals are smaller than the CF radicals, and thus, deeply penetrate the contact hole and etch the silicon nitride film.